Method of cleaning heat exchanger surfaces



Patented July 10, 1945 UNITED .STAT

EsPAr ENTY omen METHOD EOFCLEANING 'HEAT- EXGHANGER v SURFACES r Y James Simpson, Linden, N. J., assignorto Stand t Qompany, a corporation ard Oil Developmen of Delaware j No Drawing. 7 Application December 11, 1941,

. .Serial No. 422,517 I j 1 Claim. j (o ice-c9) This invention relates to the art of cleaningof metallic; ceramic and other surfaces fouled through contact with heated petroleum products inpetroleum refinery processes. The invention relates particularly to the cleaning of petroleum refinery heatexchanger surfaces by the use of solvents such as furfural. I

The processingofpetroleum hydrocarbons such as distillation; condensation and cracking involves contacting the oil with heated surfaces of metal, ceramic materials and other materials. The cracking ofthe higher hydrocarbons, for xample; usually involves preheating the oil toas high a temperature as possible by heat exchange 1 with reaction products, thenheating to about incipient cracking by passing through tubes subiect to the direet heatingefi'ect of furnace gases, then passing to a zone of high'er temperature wherein; the thermal breakdown'of the feed stock largely occurs. The products of the reaction are, as previously mentioned, passed through heat exchanger equipment to utilize the sensible heat in preheating the fresh feed. In such processing the temperature differential between the oil film upon the heat exchanger surface and the body of the liquidis-considerable;especially in the steps refinery processing. In the firstplace, th'e deposition acts as an insulating material and thus reduces considerably the heat conductivity.

Furthermore, the initial formation of a deposit acts as an accelerator in the decomposition of the oil at the surface. on the surface, the material serves as an absorbent for further quantities of oil and thus causes a very rapid increase in coke formation. The removal, therefore, of coke and the highly carbonaceous materials as soon after formation as conveniently possible is highly desirable. The present invention is directed to a simple and effective means of cleaning heat exchanger surfaces, distillation towers, etc. of petroleum refinery equipment without the necessity of dis- Once the coke is formed for cleaning the surfaces.

mantling or the undertaking of-any mechanical work. I I

The method of cleaning the surfaces is to-employ a solvent for the removal of the highly carbonace'ous binding .materials in the deposit formed onthe surface. The solvents employed are those which, as a class, haveapreferential I for the aromatic type'of hydrocarbons,

solvency suchas'furfural, phenol, nitrobenzene, chlorex, aniline," etc, of-whichfurfural, nitrobenzene and phenol are preferred. Particularly efiectiveand outstanding in its effect of cleaningpetroleum refinery heat exchanger surfaces is furfural.

The solvents may be utilized in several ways I The solvents may be applied to the surface wholly in liquid phase as',

for example, bypassing a body of the liquid",

over the surface fora'certain periodiof time; or it maybe utilized partly in the liquidpand partly I in the vapor form by evaporating the solvent,

either in an external vessel orwithin the structure to be cleaned and then p rmitting the vapors to be condensed thereon; or. its combination in the, vapor or liquidstate with steam by vaporiz ing the solvents in thepresence of steam andcontacting the equipment with the mixture; When the surface of the equipment to be cleaned isa'lso contaminated with heavy hydrocarbons, it is usual to Wash first the fouled surface with a light hydrocarbon to remove as much of the heavy hydrocarbons as possible and then to circulatethe cleaning solvent through the equipment at a temperature of 200 F. or higher; the temperature of treatment being determined by the nature of the solvent employed, especially its solvency and boiling point, and by the resistance of the deposit to the resolution.

In one form of the invention as applied to the cleaning of heat exchange equipment used in preheating a. distillate feed to a cracking coil,

the preferred method consists in disconnecting the exchanger feed lines and washing the surfaces with a light naphtha. The exchanger is then connected to a furfural reservoir, a pump and a heating'coil. The furfural is pumped from the reservoir through the heating coil where it is at least partially vaporized and then through the heat exchanger. The furfural then passes to the reservoir and is recycled through the exchanger until the carbonaceous material has been loosened from the metallic surfaces and largely removed.

If desired, a filter may be included in the circuit to remove the insoluble carbon. The exchanger is then'fiushed with an-additional quantity of light naphtha to recover completely the furfural appreciable I solvent and to wash out further quantities of carbon which may be loosened from the exchanger surfaces but still remaining in the exchanger. In a further embodiment of the invention the cleaning of distillation equipment is generally efiected by vaporizing the solvent, generally furfural, in, the still and then allowing thevapors to condense upon the fouled surfaces/ In general, the contacting of the fouled surfaces with furf ural for about an hour is usuall satisfactory, but this period may be longer or shorter depending upon the actual nature of the deposit to be removed. In the use of furfural, it is noticeable that the heavy hydrocarbon are extracted from the deposit and the coke is left in a granu lar and easily removable form. Sometimes it is advantageous to employ a light hydrocarbon solvent, such as a solvent naphtha, to remov'ei'the' granular coke after the treatment with furfural.

It has been found with furfural that the liquid maybe used many times 'inthe cleaning of the equipment but that ultimately it becomes; satto pass the cooled liquid through a filter before using-asecond time. a

Y It;is appreciatedthat in theprior art, heat exchanger surfaces have been cleaned by procedures similar .to that-of the present invention. In'the prior art it has-been known to employ solvents forlthe asphaltenes and carbenes suchas carbon disulfidel and carbon tetrachloride and to cornbinegthe use of such liquids with the action of abrasives.

particularlyfurfural, is distinguishable from these Thepresent of solventliquids having a selective solvency for aromatics, and

prior art processes in the much more advantageous effect accomplished by the use of the solvents of this type. The reason for the particular effectiveness of the solvents of this invention is not definitely known but actual processing has demonstrated the higher capacity of the solvents of this invention over those previously employed for the highly carbonaceous materials binding the carbon to the heat exchanger surfaces. Furthermore, the carbon, after the removal of the highly carbonaceous binding agent, is easily removable by mechanical means and even by washing with a light hydrocarbon liquid.

'lfrom results obtained with various solvents,

it seems clear that the heavy oil acting to cement the carbonaceous deposit together is highl aromaticin nature and is appreciably more soluble "ifr'solvents having a preferential solubility for aromatics than in asphalt solvents. If a badly cokedsurface is subjected to an extensive washing wi'thsolvents such as carbon diSlllfide; carbon tetrachloride; naphtha, etc., only a portion of the carbon will be loosened-and washed fromsthe surfacega Washing withphenol, nitrobenzene; aniline, cresol, beta, beta dichlorethyl ether, etc., will remove a major portion of the coke but washing with furfural as the most-effective solvent of thegroup. will remove substantiallyall.

Althou ghrthe present invention has: been described inpconnection with specific applications thereof, it is not intended that the application shall be limited thereby, but shall be determined solely bythe following claim or its equivalents.

What is claimed: is: I

A process" for'cleaning surfaces of petroleum refinery distillation equipment contaminated by highly. caribonaceous material and bonded by heavy-hydrocarbons soluble in solvents for are-- matic -type hydrocarbons whichconsists in- Washing saidsurfaceswith a light petroleum naphthaito-remove as much as possible of the heavy hydrocarbons, then vaporizing furfural insaid distillation equipment, allowing the fur,- fural vapor tocondense-upon the fouled surfaces, and mechanically treating the said surfaces to remove-janwadherent solid material.

-- JAMES SIMPSON. 

